Photoconductive layer refresh

ABSTRACT

In one implementation, an image forming apparatus may include a photoconductive unit and a refresh unit. The photoconductive unit may include a photoconductive layer. The photoconductive layer may have a first polarity during a print routine. The refresh unit may apply a voltage to the photoconductive layer to electrically bias the photoconductive layer to have a second polarity during a refresh routine.

BACKGROUND

Electrophotography is commonly used in digital printers or presses.Digital printing may use a variety of print material to reproduce avariety of digital sources on a variety of media. Digital printers orpresses may utilize a photoconductor to apply print material to a printmedium. The photoconductor may be charged and exposed to light. Chargedprint material, such as toner, may be attracted to areas of thephotoconductor. The print material may be transferred from thephotoconductor to the print medium directly or to an offset unit. Heatand/or pressure may fuse the toner to the medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are block diagrams of examples of image forming apparatus.

FIGS. 3 and 4 depict components for implementing various examples.

FIGS. 5 and 6 depict states during example operations of variousimplementations of an image forming apparatus.

FIGS. 7 and 8 are flow diagrams depicting example methods for lesseninga contamination effect.

DETAILED DESCRIPTION

In the following description and figures, some example implementationsof an image forming apparatus, systems, and/or methods are described. Animage forming apparatus using electrophotography may have a constant orintermittent charge on a photoconductor during a print routine, or printcycle. After completing a number of print cycles over a time period, thephotoconductor may obtain characteristics, or polarization effects, thatmay decrease print quality. For example, the photoconductor may becomeionized, change in molecular structure, may trap charges, or may showsigns of lateral conductivity. These contamination effects, includingpolarization effects, may make it difficult to accurately affix printmaterial to a print article or medium. The print medium may include anintermediate transfer member. Print quality may be improved bymaintaining the photoconductor with a routine that may lessen an effectof contamination.

Various examples described below were developed to lessen the effects ofbiasing a photoconductor to one polarity. By scheduling time to refreshthe photoconductor by charging the photoconductive layer of thephotoconductive unit to a polarity opposite of the polarity of thephotoconductive layer during a print cycle, the effects of polarizationfrom charging in one polarity may be diminished.

FIGS. 1 and 2 are block diagrams of examples of image forming apparatus.Referring to FIG. 1, an example image forming apparatus 100 may includea refresh unit 102 and a photoconductive unit 104.

In general, the photoconductive unit 104 may include a photoconductivelayer 106. For example, the photoconductive unit 104 may be an organicphotoconductor. The photoconductive layer 106 may be configured to applya print material to a print article. The print material may be directlyapplied to the print article or indirectly applied by using an offsetunit, or an intermediate transfer member, for transferring the printmaterial. An offset unit may be any intermediate transfer member capableof transferring the print material from the photoconductive unit 104 tothe print article. The photoconductive layer 106 may be capable of beingelectrically biased to have a first polarity during a print routine. Thephotoconductive layer 106 may be capable of being electrically biased tohave a second polarity during a refresh routine. The refresh routine maybe a non-print routine to occur when the image forming apparatus 100 isnot in a print mode. The image forming apparatus 100 may be operable ineither a refresh mode or a print mode.

The refresh unit 102 may be configured to apply a voltage 113 to thephotoconductive layer 106 of the photoconductive unit 104 toelectrically bias the photoconductive layer 106 to have a secondpolarity during the refresh routine. The voltage 113 may polarize thephotoconductive layer 106 to a polarity that is opposite of the polarityof the photoconductive layer 106 during a print routine. For example,the first polarity may be negative and the second polarity may bepositive. The voltage may be supplied by direct current (“DC”),alternating current (“AC”), pulsating current, variable current, or acombination of currents capable of polarizing the photoconductive layer106. “Voltage,” such as voltage 113, may be discussed as a “refreshvoltage,” or in conjunction with another modifier to denote the sourceof the voltage, but may otherwise have the same characteristics of othervoltages described herein.

The voltage 113 may achieve an avalanche threshold. The avalanchethreshold may represent the strength of the electric field, or potentialgradient, to form a conductive region around the conductor. Inparticular, the avalanche threshold may be based on a function defininga point at which the gas or fluid around the conductor ionizes to forman electron avalanche. The gas or fluid around the conductor may be air.

One example of a charge that may produce an electron avalanche is acorona charge. A corona charge may have an electric field with thestrength sufficient to ionize a neutral atom where the energy ofelectric field may accelerate oppositely charged particles in oppositedirections at a velocity high enough to collide with and ionize anotheratom. This may repeat until a certain distance is reached where theelectric field strength may be low enough to no longer providesufficient energy to continue ionizing more atoms.

The avalanche threshold may be based on the distance between twosurfaces, or gap length. For example, the avalanche threshold may bedetermined based on a function of an electric field strength and a gaplength between the photoconductive layer and a charge surface; thecharge surface may be part of charge mechanism that may apply therefresh voltage to the photoconductive layer. The electric field maybecome low enough at a distance from the conductor that the electricfield may not provide enough energy to ionize the air at that distance.For example, a 1000 volt charge may achieve the avalanche threshold inair over a gap length of 1 mm, but may not achieve the avalanchethreshold in air over a gap length of 10 cm.

A voltage at or above the threshold based on the gap length may lessenthe effect of polarization and/or contamination on the photoconductivelayer 106. For example, if an avalanche threshold is 600 volts, theavalanche threshold may be achieved by meeting the threshold by applying600 volts or by surpassing the threshold by applying more than 600volts. The avalanche threshold may be based on corona charging,Paschen's law, or other studies or experiments providing a minimumvoltage to apply between two surfaces to form an electron avalanche.

Referring to FIG. 2, an example image forming apparatus 200 may includea refresh unit 102 and a photoconductive unit 104. The refresh unit 102may include at least one of a charge unit 220 and an intermediate unit210. The photoconductor unit 104 may include a photoconductive layer 106and a conductive layer 108. The photoconductive layer 106 may be capableof being electrically biased to have a first polarity during a printroutine.

The charge unit 220 may be operatively coupled to the photoconductiveunit 104. The charge unit 220 may charge the photoconductive layer 106to a print polarity during a print routine while the image formingapparatus 200 is in a print mode. The refresh unit 102 may charge thephotoconductive layer 106 to a refresh polarity during a refresh routinewhile the image forming apparatus 200 is in a refresh mode. The refreshpolarity may be opposite of the print polarity.

The refresh unit 102 may be operatively coupled to the photoconductiveunit 104. The refresh unit 102 may include a charge mechanism toelectrically bias the photoconductive layer 106 of the photoconductiveunit 104 to have a polarity opposite of the print polarity. The refreshunit 102 may be a unit dedicated to providing a charge to thephotoconductive layer 106 during the refresh routine or may include atleast one of the charge unit 220 and/or the intermediate unit 210. Forexample, the refresh unit 102 may be the charge unit 220 and the chargeunit 220 may be capable of both charging the photoconductive layer 106to a negative polarity during the print routine and charging thephotoconductive layer 106 to a positive polarity during the refreshroutine. The intermediate unit 210 may be any chargeable component of animage forming apparatus capable of transferring a charge to thephotoconductive layer 106 to electrically bias the photoconductive layer106 to have a polarity opposite the polarity of the photoconductivelayer 106 during the print routine. For example, FIG. 4 shows adevelopment unit 312, a transfer unit 310, an offset unit 420, a spongeunit 422, and the conductive layer 108 of the photoconductive unit 104and the intermediate unit 210 may be at least one of a development unit312, a transfer unit 310, and offset unit 420, a sponge unit 422, andthe conductive layer 108 of the photoconductive unit 104.

The charge unit 220 may be configured to apply a voltage 113 to thephotoconductive layer 106 of the photoconductive unit 104. The voltage113 may electrically bias the photoconductive layer 106 to have apolarity opposite the polarity of the photoconductive layer 106 during aprint routine. The voltage 113 may achieve an avalanche threshold. Thecharge unit 220 may apply the voltage 113 during a refresh routine.

The intermediate unit 210 may be operatively coupled to thephotoconductive unit 104 and may be configured to apply the voltage 113to the photoconductive layer 106 of the photoconductive unit 104. Theintermediate unit 210 may be charged to electrically bias thephotoconductive layer 106 to a polarity opposite the polarity of thephotoconductive layer 106 during a print routine by applying the voltage113 to the photoconductive layer 106 during the refresh routine. Thevoltage 113 may achieve an avalanche threshold. The intermediate unit210 may or may not have a charge during the print routine. For example,the charge unit 220 may charge the intermediate unit 210 using a voltage215 to allow the intermediate unit 210 to apply the voltage 113 to thephotoconductive layer 106.

The refresh unit 102 may consist of a plurality of components capable ofproviding a refresh charge to the photoconductive layer 106. For examplein FIG. 2, a refresh unit 102 may include a charge unit 220 and anintermediate unit 210. Each one of the plurality of components mayprovide a charge to the photoconductive layer 106 and the charges of theplurality of components may aggregate to the refresh voltage 113 toelectrically bias the photoconductive layer 106 to have a polarityopposite of the polarity of the photoconductive layer 106 during a printroutine. For example during an example refresh routine, the charge unit220 may apply a charge 219 to the photoconductive layer 106 and theintermediate unit 210 may apply a charge 217 to the photoconductivelayer 106. The combination of the charges 217 and 219 may have voltagesthat aggregate to be the refresh voltage 113 and the aggregate voltagemay achieve the avalanche threshold. The charges 217 and 219 may bothachieve the avalanche threshold, one of the charges 217 and 219 mayachieve the avalanche threshold, or neither charge 217 nor charge 219may achieve the avalanche threshold alone, but may achieve the avalanchethreshold together. For example, if the avalanche threshold is 1100volts, the intermediate unit 210 may provide a charge 217 of 600 voltsand the charge unit 220 may provide a charge 219 of 600 volts so thatthe total refresh voltage 113 combines to be 1200 volts, which surpassesthe avalanche threshold.

FIGS. 3 and 4 depict components for implementing various embodiments.Referring to FIG. 3, an example image forming apparatus 300 maygenerally comprise a charge unit 220, a photoconductive unit 104, atransfer unit 310, a development unit 312, and a light source 314. Thephotoconductive unit 104 may include a photoconductive layer 106 and aconductive layer 108.

During a print routine, the charge unit 220 may charge thephotoconductive layer 106. The conductive layer 108 may have a polarityin relation to the charge on the photoconductive layer or may begrounded. The charge unit 220 may apply a print voltage to electricallybias the photoconductive layer 106 to have a print polarity during theprint routine. For example, the charge unit 220 may use a corona chargeto ionize the air between the charge unit 220 and the photoconductiveunit 104 to repel electrons to the photoconductive layer 106. Thephotoconductive layer 104 may act as an isolator due to the charge. Thelight source 314 may apply light to the photoconductive layer 106 tomake a portion of the photoconductive layer 106 conductive. Theconductive portion of the photoconductive layer 106 may not be chargedand may not attract print material. The development unit 312 may apply aprint material, such as toner, to the charged areas of thephotoconductive layer 106. The photoconductive layer 106 may apply aprint material from the development unit 312 to a print article 318using the transfer unit 310. The print voltage may be the voltage usedby the photoconductive layer 106 during a print routine to maintainoperability for printing.

One or more print routines may cause the photoconductive layer 106 to becontaminated. Contamination may affect the photoconductive layer 106 tobe conductive when the desired effect of photoconductive layer 106 maybe to act as an isolator. Contamination may be any polarization effect,including lateral conductivity, ionization, ion migration, a molecularstructure change, an electron trap, or a polarized contaminant particlebeing attracted to the photoconductive layer 106. The effects ofcontamination on the printed image may include streaking, scratching,blurring, and/or other detriments to print quality.

A refresh routine may be scheduled to temper, dull, deaden, reverse,curtail, screen, or otherwise lessen the effects of contamination and/orpolarization. The refresh routine may be scheduled before a printroutine, while a print routine is paused, or after a print routine iscompleted. The refresh routine may be scheduled based on at least one ofa time elapsed, a print cycle amount, and a level of contamination. Aprint cycle amount may include one or more print routines. A level ofcontamination may be based on a tolerance setting in comparing a printarticle to the original image or detecting an amount of contaminationabove a contamination threshold.

A refresh unit may execute opposite polarity charging on thephotoconductive layer during a refresh routine when the image formingapparatus 300 is in a refresh mode. In one example as described inrelation to FIG. 3, the refresh unit may be the charge unit 220configured to charge the photoconductive layer 106 to both positive andnegative polarities depending on what mode the image forming apparatus300 is operating and/or which routine is being executed.

A firmware module 316 may be in communication with the componentdesignated to charge the photoconductive layer 106 to schedule a refreshroutine, set a time period to execute the refresh routine, and set alevel of the voltage applied by the designated component, such as thecharge unit 220 in FIG. 3. A firmware module 316 may comprise anycombination of physical and logical components, such as circuitry andinstructions on memory, to manage operations of the image formingapparatus 300 designated to the firmware module 316. The firmware module316 may communicate to the charge unit 220 to switch charging polaritiesdepending on the operation mode and/or the routine performed. Thefirmware module 316 may designate which component may charge thephotoconductive layer 306.

During a refresh routine, the component designated by the firmware tocharge the photoconductive layer 106, such as the charge unit 220 inFIG. 3, may apply a refresh voltage to charge the photoconductive layer106 of the photoconductive unit 104. The refresh voltage mayelectrically bias the photoconductive layer 106 to have a refreshpolarity opposite of the print polarity. For example, the print polaritymay be negative and the refresh polarity may be positive. The refreshvoltage may achieve an avalanche threshold by applying a voltageequivalent to the avalanche to the photoconductive layer 106 or applyinga voltage exceeding the avalanche to the photoconductive layer 106.

Referring to FIG. 4, an example image forming apparatus 400 maygenerally comprise a charge unit 220, a photoconductive unit 104, atransfer unit 310, a development unit 312, a light source 314, afirmware module 316, an offset unit 420, and a sponge unit 422. Theimage forming apparatus 400 may also include a refresh unit 102. Thephotoconductive unit 104 may include a photoconductive layer 106 and aconductive layer 108. The image forming apparatus 400 may be operable ina print mode and a refresh mode. The image forming apparatus 400 mayperform a print routine in a print mode, switch to a refresh mode,perform a refresh routine, and switch back to a print mode.

During a print routine, the charge unit 220 may charge thephotoconductive layer 106. The charge unit 220 may apply a print voltageto electrically bias the photoconductive layer 104 to have a polarityduring the print routine. For example, the charge unit 220 may beoperatively coupled to the photoconductive unit 104 to apply a voltageto the photoconductive layer 106 to charge the photoconductive layer 106to a polarity during a print routine, such as a negative polarity. Thelight source 314 may neutralize areas of the photoconductive layer 106and the charged areas of the photoconductive layer 106 may attract tonerfrom the development unit 312. The sponge unit 422 may apply a dampeningsolution to the photoconductive layer 106 or may otherwise utilize asubstrate to clean the photoconductive layer 106. The offset unit 420may receive the toner from the photoconductive layer 106 and apply thetoner to a print article 318 using the transfer unit 310.

A refresh unit 102 may be operatively coupled to the photoconductiveunit 104 to apply a refresh voltage to the photoconductive layer 106 tocharge the photoconductive layer 106 to a positive polarity during arefresh routine. The refresh voltage may achieve an avalanche thresholdbased on the gas inside the image forming apparatus 400 and the gaplength between the photoconductive layer 106 and the refresh unit 102.The gas within the image forming apparatus 400 may be air.

Alternatively, the image forming apparatus 400 may use one or more ofthe other components to operate as the refresh unit 102. For example,the refresh unit 102 may be at least one of the charge unit 220, theoffset unit 420, the development unit 312, the sponge unit 422, theconductive layer 108 of the photoconductive unit 104, or any other unitthat is operatively coupled to the photoconductive unit 104 to chargethe photoconductive layer 106. The components of the image formingapparatus 400 may be electrically coupled over an electrical connection426 to provide a charge from one component to another. The electricalconnection 426 may provide a degree of electrical coupling between acomponent providing a charge and the component receiving a charge.

The refresh voltage may be a combination of voltage from one or more ofthe components of the image forming apparatus 400 that are coupled tothe photoconductive unit 104 to charge the photoconductive layer 106 toan opposite print polarity, such as a positive polarity, during arefresh routine. For example during the refresh routine, the offset unit420 may be operatively coupled to the photoconductive unit 104 to chargethe photoconductive layer 106 with an offset unit charge, or a chargefrom the offset unit, where the offset unit voltage of the offset unitcharge may meet or exceed an avalanche threshold and may charge thephotoconductive layer 106 to a positive polarity. For another exampleduring the refresh routine, the charge unit 220 and the offset unit 420may be operatively coupled to the photoconductive unit 104 to charge thephotoconductive layer 106; the charge unit 220 may apply a charge unitvoltage and the offset unit 420 may apply an offset unit voltage wherethe combination of the charge unit voltage and the offset unit voltagemay achieve the avalanche threshold. In that example, the charge unitvoltage or the offset unit voltage alone may not achieve the avalanchethreshold, but the combination of voltage may achieve the avalanchethreshold. Generally, the combination of voltage may include one voltageand/or charge from a single unit. The terms of “charge unit voltage” and“offset unit voltage” are used to distinguish the source of the voltage,but the voltages may not otherwise be different.

FIGS. 5 and 6 depict states during example operations of variousimplementations of an image forming apparatus. In particular, FIG. 5provides examples of operation states of the refresh unit 102, thephotoconductive layer 106, and the conductive layer 108 before, during,and after a refresh routine and FIG. 6 depicts an example voltagetransition of the charge unit and the photoconductive layer during arefresh routine between two print routines.

Referring to FIGS. 5 and 6, the components of the image formingapparatus may be in state of operation having a particular polarity atany given time in a print mode or refresh mode. For example, thepolarity of the photoconductive layer 106 may be negative prior toexecution of a refresh routine in a refresh mode in conjunction with theprint voltage provided by the charge unit during a print routine. Theconductive layer 108 may be polarized or may be grounded in accordancewith the requirements of the print routine. The photoconductive layer106 may be affected by contamination prior to execution of a refreshroutine. For example, the photoconductive layer 106 may be affected bylateral conductivity 510 and may have a polarized particle 508 attractedto the photoconductive layer 106 as shown as state A in FIG. 5.

In an example state, such as state B, the image forming apparatus mayswitch to a refresh mode and initiate a refresh routine. The refreshunit 102 may charge to a state having a polarity opposite the polarityof the photoconductive layer 106 during the print routine. For example,if the photoconductive layer 106 is charged negatively during the printroutine, the refresh unit 102 may prepare to charge the photoconductivelayer 106 to have a positive polarity during the refresh routine. Thevoltage of the refresh unit 102 may change in accordance with thispreparation. For example, as shown in FIG. 6, the refresh unit 102 mayswitch to producing a positive polarity during a refresh mode if thephotoconductive layer 106 is charged negatively during print mode.

In an example state during the refresh mode, such as state C, therefresh unit 102 may charge the photoconductive layer 106 to a polarityopposite the polarity of the photoconductive layer 106 during the printroutine. The refresh unit 102 may charge the photoconductive layer 106by ionizing the air between the refresh unit 102 and the photoconductivelayer 106. The effects of charging the photoconductive layer 106 to aparticular polarity during the print routine may be diminished,screened, or removed by changing the electrical bias of thephotoconductive layer 106 to charge the photoconductive layer 106opposite to the polarity during the print routine. For example in stateC of FIG. 5, the polarized particle 508 may be repelled by the change inpolarity and the lateral conductivity may be removed by the change inpolarity. The refresh unit 502 may charge the photoconductive layer 106for a designated amount of time based on the level of contamination, atime period elapsed, and/or the amount of consecutive print cycles sincethe last refresh routine. The designated amount of time may be less thana damage threshold to avoid adversely affecting the condition of thephotoconductive layer 106 based on the material and/or condition of thephotoconductive layer 106.

In another example refresh routine state, such as state D, the refreshunit 102 may change voltage and polarity in preparation for a printroutine. For example, the refresh unit 102 may neutralize or begincharging in a polarity used during the print routine, such as a negativepolarity. The photoconductive layer 106 may continue to be charged tothe opposite polarity, such as in state D; may be neutralized; or may becharged to the print polarity in preparation for a print routine; suchas in state E. The diminishing, screening, or removal of thecontamination may refresh the photoconductive layer 106 to produce animproved print quality in comparison to before the execution of therefresh routine.

FIGS. 7 and 8 are flow diagrams depicting example methods for lesseninga contamination. In discussing FIGS. 7 and 8, reference may be made toelements and diagrams of FIGS. 1-6 to provide contextual examples.Implementation, however, is not limited to those examples.

In block 702, a refresh routine of an image forming apparatus may beinitiated. The image forming apparatus may include a photoconductiveunit having a conductive layer and a photoconductive layer to apply aprint material to a print article. Each one of the components of theimage forming apparatus may be neutralized, powered off, or otherwiseplaced in an electrical state to allow the photoconductive layer to becharged during the refresh routine.

In block 704, a refresh voltage may be applied to the photoconductivelayer to electrically bias the photoconductive layer to have a refreshpolarity opposite of a print polarity. The refresh voltage may achievean avalanche threshold.

The avalanche threshold may be determined based on an electric fieldstrength and a gap length. The gap length may be between thephotoconductive layer and the charge surface. The charge surface may beon a charge mechanism applying the refresh voltage to thephotoconductive layer. The charge mechanism may be at least one of arefresh unit, the charge unit, and an intermediate unit. Another factorto determine the avalanche threshold may be the pressure of the gas inthe area of the gap length.

Referring to FIG. 8, the discussion and description of blocks 702 and704 may be applied to blocks 808 and 810 respectively.

In block 802, a refresh routine may be scheduled based on at least oneof a time elapsed, a print cycle amount, and a level of contamination.The firmware module may schedule the refresh routine.

The image forming apparatus may be operable in a print mode and in arefresh mode. The refresh routine may be scheduled by manually selectinga refresh mode of the image forming apparatus or by dynamicallyselecting the refresh mode using a function based on at least one of atime elapsed, a print cycle amount, and a level of contamination.

In block 804, a print routine of the image forming apparatus may becompleted while in a print mode. The firmware module may wait for anycurrent print cycles to complete before performing a refresh routine ormay interrupt the print routine to allow the refresh routine to execute.

In block 806, the image forming apparatus may switch from a print modeto a refresh mode. The firmware module may restrict enablement of therefresh mode for non-print routines. For example, the refresh mode maybe available during a time period that no print cycles are beingexecuted, or a non-print time in the print cycle, such as a pause in theprint routine.

In block 808, the firmware module may initiate a refresh routine whilein the refresh mode.

In block 810, a refresh voltage may be applied to the photoconductivelayer to electrically bias the photoconductive layer to have a refreshpolarity opposite of the print polarity. For example, the print polaritymay be negative and the refresh polarity may be positive. The refreshvoltage may be applied from the intermediate unit, multiple intermediateunits, or a combination of the charge unit and one or more intermediateunits. The one or more intermediate units may be charged to provide therefresh voltage. The combination voltage may achieve the avalanchethreshold. The combination voltage may be one voltage from a single unitto apply the entire refresh voltage or the aggregate of voltages frommultiple units. The refresh routine may apply the refresh voltage for apredetermined and/or calculated amount of time.

In block 812, the image forming apparatus may switch from the refreshmode to the print mode. For example, once the refresh routine iscompleted, the image forming apparatus may prepare for a print routineby completing all functions associated with the refresh routine andswitch to a print mode.

Although the flow diagrams of FIGS. 7 and 8 illustrate specific ordersof execution, the order of execution may differ from that which isillustrated. For example, the order of execution of the blocks may bescrambled relative to the order shown. Also, the blocks shown insuccession may be executed concurrently or with partial concurrence. Allsuch variations are within the scope of the present invention.

The present description has been shown and described with reference tothe foregoing exemplary embodiments. It is understood, however, thatother forms, details, and embodiments may be made without departing fromthe spirit and scope of the invention that is defined in the followingclaims.

What is claimed is:
 1. An image forming apparatus comprising: aphotoconductive unit including a photoconductive layer, thephotoconductive layer electrically biased to have a first polarityduring a print routine; and a refresh unit to apply a voltage to thephotoconductive layer to electrically bias the photoconductive layer tohave a second polarity during a refresh routine, the voltage to achievean avalanche threshold and the second polarity to be opposite of thefirst polarity.
 2. The image forming apparatus of claim 1, wherein therefresh unit is at least one of a charge unit and an intermediate unit.3. The image forming apparatus of claim 2, wherein the intermediate unitis at least one of a development unit, a transfer unit, an offset unit,a sponge unit, and a conductive layer of the photoconductive unit. 4.The image forming apparatus of claim 1, further comprising a firmwaremodule in communication with the refresh unit, the firmware module toschedule the refresh routine, set a time period to execute the refreshroutine, and set a level of the voltage applied by the refresh unit. 5.The image forming apparatus of claim 1, wherein the first polarity isnegative, the second polarity is positive, and the refresh routine is anon-print routine.
 6. An image forming apparatus comprising: aphotoconductive unit including a photoconductive layer; a charge unitcoupled to the photoconductive unit to apply a print voltage to thephotoconductive layer to charge the photoconductive layer to a firstpolarity during a print routine; and a refresh unit coupled to thephotoconductive unit to apply a refresh voltage to the photoconductivelayer to charge the photoconductive layer to a second polarity during arefresh routine, the second polarity opposite of the first polarity andthe refresh voltage to achieve an avalanche threshold.
 7. The imageforming apparatus of claim 6, wherein the refresh unit is at least oneof the charge unit, an offset unit, a development unit, a sponge unit,and a conductive layer of the photoconductive unit and the refreshvoltage is a combination of voltages from the at least one of the chargeunit, the offset unit, the development unit, the sponge unit, and theconductive layer of the photoconductive unit.
 8. The image formingapparatus of claim 7, comprising the offset unit coupled to thephotoconductive unit to charge the photoconductive layer with an offsetunit voltage during the refresh routine.
 9. The image forming apparatusof claim 8, wherein the charge unit charges the photoconductive layerwith a charge unit voltage and the combination of voltage includes thecharge unit voltage and the offset unit voltage, the combination ofvoltage to achieve the avalanche threshold.
 10. A method for lessening acontamination effect comprising: initiating a refresh routine of animage forming apparatus, the image forming apparatus including aphotoconductive unit having a photoconductive layer; and applying arefresh voltage to the photoconductive layer to electrically bias thephotoconductive layer to have a refresh polarity opposite of a printpolarity, the refresh voltage to achieve an avalanche threshold.
 11. Themethod of claim 10, wherein the avalanche threshold is determined basedon an electric field strength and a gap length between thephotoconductive layer and the charge surface of a charge mechanism, thecharge mechanism to apply the refresh voltage to the photoconductivelayer.
 12. The method of claim 11, wherein the charge mechanism is atleast one of a refresh unit, the charge unit, and an intermediate unit.13. The method of claim 12, further comprising charging the intermediateunit to electrically bias the photoconductive layer.
 14. The method ofclaim 10, further comprising scheduling a refresh routine based on atleast one of a time elapsed, a print cycle amount, and a level ofcontamination.
 15. The method of claim 10, further comprising:completing a print routine of the image forming apparatus in a printmode, the image forming apparatus operable in the print mode and arefresh mode; and switching from the print mode to the refresh mode.